1. Field of the Invention
The present invention relates to a method for analyzing loop interface failures and a system having a function of analyzing loop interface failures.
2. Description of the Related Art
Recently, an interface which connects devices in a loop such as a Fibre Channel Arbitrated Loop (FC-AL) has been widely used in disk array apparatuses and the like, since it has a simple connecting configuration of cables and can easily accommodate device extensions. However, this type of interface has such a problem that, when signals cannot propagate in the loop because of failures or the like in interface circuits of connected devices (this is called, for example, loop abnormality or link down), the whole loop cannot be used. That is, even though a failure occurs in only one device, all devices connected to the loop cannot be used. In order to cope with this problem, disk array apparatuses usually have interface circuits for two ports, so that these devices are connected to two independent loops. With this configuration, even when one loop of the dual loop interfaces is out of use because of a failure or the like, accesses can be performed using the other loop, to thereby improve reliability. Further, this kind of disk array apparatus has a function of identifying a faulty device and restoring the failure when a loop abnormality occurs.
As an example, the Japanese Patent Application Laid-open No. 2002-7077 discloses a disk array apparatus having two FC-ALs, or loops A and B. In this example, when an abnormality occurs in the loop A, a disk controller in the loop A stops the normal disk processing and transits to a temporary degenerate state, and the loop B acts the processing for the loop A. The disk controller in the loop A performs a diagnosis of the loop A by itself and bypasses the faulty device from the loop A to thereby clear the temporary degenerate state of the loop A. With this structure, it is possible to identify a faulty component while keeping response to the host, when a loop abnormality occurs. However, in the aforementioned example, a loop abnormality is supposed to be an intermittent failure. Therefore, it is assumed that the loop A is not abnormal at the time of diagnosing the loop A.
As another example, the Japanese Patent Application Laid-open No. 2001-216206 discloses a method for analyzing failures, which is applicable to disk array apparatuses having two FC-ALs, or loops A and B, in which an enclosure service device directly connects to each loop. An enclosure service device is a device for monitoring the environment inside of the casing and managing resources of a device which conforms to the ANSI Standard (NCITS 305-199X). The device also has a function of controlling a loop connection switching unit which performs bypassing or releasing the bypass of disks connecting to the loop, to which the device itself connects. The enclosure service device directly connecting to the loop acts as a device connecting to the loop interface as same as the disk connecting to the loop. Therefore, when a unique failure occurs in the loop to which the enclosure service device connects, the disk controller of the loop cannot instructs the enclosure service device through the loop. In order to cope with this problem, in the aforementioned example, an interface is provided between the enclosure service devices connecting to respective loops. The interface works in such a manner that when a failure occurs in the loop A, it instructs the enclosure service device in the loop A to bypass or release the bypass of disks in the loop A, via the enclosure service device in the loop B, for diagnosing the loop A.
As described above, in the system of disk array apparatus having a loop interface such as an FC-AL, the reliability is improved by using dual loop interfaces and bypassing faulty components through an immediate failure analysis at the time of loop abnormality. However, in the system in which enclosure service devices directly connect to respective loops, some other problems arise as described below, when loop failures occur in the both loops of the dual loop interfaces at the same time.
A first problem is that the devices connecting to the loop interfaces cannot be detached from or reconnected to the loops at all, since the enclosure service devices for controlling the loop connection switching units, which actually perform detachment and reconnection, cannot be accessed from either loop.
A second problem is that a loop diagnosis for identifying faulty devices, which cause the loop abnormalities, cannot be performed. In order to perform the loop diagnosis, the devices connecting to the loop interfaces must be detached from and reconnected to the loops. However, the detachment and the reconnection cannot be performed in the system.
A third problem is that the system remains completely stopped, since the loop diagnosis cannot be performed so that faulty components cannot be removed from the loops.